1. Field
Aspects of the present invention generally relate to open/close sensing of a door for accessing an internal portion of an image forming apparatus.
2. Description of the Related Art
In general, an image forming apparatus such as a copier has a mechanism that allows a user to open a door of an apparatus to access an internal portion of the apparatus in a case of removing recording paper that has been stuck in a conveying path, a case of replacing a process cartridge, or other such case. Such an image forming apparatus includes an interlock mechanism for mechanically interrupting power supply to a driving mechanism such as a motor and a high-voltage circuit when the door is opened. Therefore, the driving mechanism stops operating when the door is opened even while the image forming apparatus is in operation, which can prevent an unexpected situation.
As a conventional technology relating to the above-mentioned interlock mechanism, there are known technologies disclosed in, for example, Japanese Patent Application Laid-Open Nos. 2009-198708 and 2007-140044. In those conventional technologies, the image forming apparatus includes a door open/close sensing sensor for sensing an open/closed state of the door and an engine controller (hereinafter referred to as “control portion”). The control portion senses that the door has been opened or closed by periodically examining an output from the door open/close sensing sensor. When sensing that the door has been opened, the control portion stops the driving mechanism, displays the open/closed state of the door on an operation portion operated by the user, and performs other such processing performed when the door is opened.
However, in the conventional technologies, the control portion can recognize the open/closed state of the door only at a timing at which the output signal output from the door open/close sensing sensor is examined by the control portion. This is because the control portion can only periodically examine a result of sensing performed by the door open/close sensing sensor. Therefore, the control portion may fail to recognize that the door has been opened if, for example, an open/close operation of the door is performed within a time interval shorter than a cycle period during which the control portion recognizes the open/closed state of the door.
In the image forming apparatus, the recording paper normally stops being conveyed when the door is opened during an image forming operation. After that, when the door is closed again, the operation portion issues a notification to instruct the user to remove the recording paper that has been stuck in the conveying path. When the recording paper is removed by the user, the image forming operation is restarted.
However, if the control portion cannot recognize that the door has been temporarily opened during the image forming operation, for example, the following problems occur.
That is, when the image forming apparatus starts the image forming operation, the control portion senses a BD signal (main-scanning synchronizing signal) in order to determine an irradiation start position in a main-scanning direction of a laser that is to irradiate a photosensitive drum. If the door is opened at this time, an interlock power source may be interrupted. In this case, the power supply to a scanner unit is stopped, which inhibits the control portion from detecting the BD signal.
If the BD signal cannot be sensed, the control portion examines the output from the door open/close sensing sensor. If the door is open, the control portion recognizes that the BD signal cannot be sensed because the door has been opened and the interlock power source has been interrupted, and discontinues the image forming operation.
However, there is a case where the door is closed even if the BD signal cannot be sensed. This is a case where the open/close operation for the door is performed before the control portion recognizes the open/closed state of the door as described above and the door is already closed when the control portion recognizes the open/closed state of the door. In this case, the control portion determines that the door is closed, and therefore erroneously recognizes that the BD signal can no longer be detected due to an occurrence of a failure in the scanner unit to stop the image forming operation. Therefore, even if the image forming apparatus is in a normal state, the user is erroneously informed that the failure has occurred in the image forming apparatus. Further, the image forming operation is stopped, which greatly impairs convenience of the user.